Doublet (lens)

In optics, a doublet is a type of lens made up of two simple lenses paired together.

Such an arrangement allows more optical surfaces, thicknesses, and formulations, especially as the space between lenses may be considered an "element".

Oiled doublets hold the optical fluid in place with surface tension alone.

[2] In a hard-cemented doublet, the lenses are held together by an adhesive with mechanical strength, such as optically transparent epoxy.

Some doublets use no adhesive between the lenses, relying on external fixturing to hold them together, either because the optical design requires a gap or because thermal expansion differences between the two lenses will not allow cementing.